The present disclosure relates to controlling the speed of a vehicle during a cruise control mode to increase fuel economy and/or emissions.
Cruise control systems are provided within vehicles to automatically control the vehicle's speed without any input, such as operation of the accelerator pedal, by the driver. Typically, a set point value related to the desired speed is defined by the driver. The vehicle speed is automatically controlled until the driver intervenes, such as by operating one or more of the brake, clutch, accelerator or mode switch.
Known adaptive cruise control systems can also provide automatic braking or dynamic set speed type controls. Automatic braking systems allow a vehicle to keep pace with the car it is following, slow when closing in on the vehicle in front and accelerate again to the threshold speed when traffic allows. Dynamic set speed uses the GPS position of speed limit signs to set the threshold speed.
Existing speed control algorithms can accurately maintain vehicle speed at the threshold speed, even under varying road gradients. However, these algorithms are not optimized for fuel economy or emissions. It is known that, even when traversing varying road gradients with gentle slopes, this can be done more economically by a skilled driver. The driver can maintain a relatively constant throttle position and allow the vehicle to accelerate on the downgrades and decelerate on upgrades, the driver reducing power when cresting a rise and increasing power before an upgrade is reached. Known cruise control systems tend to over-throttle on the upgrades and retard on the downgrades, thus wasting the energy available from the inertia of the vehicle.
Internal combustion engines operate most efficiently in terms of brake specific fuel consumption (BSFC) at a particular combination of engine speed, and torque. However, when cruising at constant speed the engine may be far from the optimal BSFC operating point.
Most speedometers have a tolerance of around ±10%. Vehicle manufacturers typically calibrate speedometers to read high by an amount equal to the average error to ensure that the speedometer does not indicate a lower speed than the actual speed of the vehicle.
Systems and methods for controlling the speed of a vehicle are provided comprising: during a pulse phase of cruise control, applying engine torque to raise speed, the amount and duration of which being responsive to engine speed; and during a glide phase of cruise control, discontinuing engine combustion. In this way cruise control may maintain a mean speed equivalent to a desired, threshold speed while reducing fuel consumption, and NVH effects compared to traditional cruise control methods.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.